1. Field of the Invention
The present invention relates to a tool holder for a disc shaped working tool such as, in particular, a cutting disc, e.g., an abrasive cutting disc. The tool holder has a working tool holding member and a counter-member rotatable, together with the working tool holding member, about an operational axis by a motor-driven power tool and cooperating with the working tool holding member for receiving therebetween the working tool for joint rotation therewith. The working tool has a central bore and at least two through-bores spaced from the central bore and each having a sharp-or continuously changing diameter over the bore length, such as, e.g., counter -or step-bores. The working tool holding member has a central opening through which in an assembled condition of the tool holder, a central securing element extends for axially securing the working tool holding member and, thereby, the working tool between the working tool holding member and the working tool holding counter-member. On the working tool holding member, there is further provided at least one coupling element radially spaced from the central opening of the working tool holding member. The at least one coupling element permits to form an eccentric rotary drive with one of the through-bores of the working tool.
2. Description of the Prior Art
Tool holders of the type discussed above provide for two basic types of securing working tool disc. With the first type, the working tool disc is simply secured to the working tool holding member with a single screw forming the central securing element. Here, the working tool disc is clamped form lockingly or frictionally between the working tool holding member and the working tool holding counter-member. The first type of fixation a disc-shaped working tool insure an easy mounting and dismounting of the working tool disc by loosening or tightening the central securing element.
With the second type, the working tool disc is tightly screwed with several screws to that of the working tool holding member and the working tool counter-holding member which is adjacent to a power tool. The heads of the screws are completely received in the counter- or step-bores which are spaced from the central bore of the working tool disc. In this way, no coupling element or elements project in the axial direction on the free side of the working tool disc. The second type of securing the working tool disc permits to provide a flush section parallel to a surface such as, e.g., floor, wall, or ceiling. Further, with this type of attachment, substantially higher torques can be transmitted or applied.
U.S. Pat. No. 4,870,946 discloses a liquid-cooled concrete saw. The saw has a flange-shaped tool holding member with a central opening and several coupling elements spaced from the central opening. The coupling elements include screws with countersunk heads and which are secured in threaded bores. Upon securing a working tool disc, the countersunk heads are received in the corresponding counter-bores of the working tool disc. Alternatively, thereto, an attachment of the working tool disc with an outer bearing plate is contemplated. The bearing plate is held on an output shaft of the concrete saw with a central screw. Thereby, the working tool disc is axially secured between the working tool holding member and the bearing plate. The working tool disc is rotated over a pin that extends from the working tool holding member and engages in an opening of the working tool disc.
With the tool holder of the U.S. Pat. No. 4,870,946, for a normal cutting operation, in order to increase the transmittable torque, besides the attachment with a central screw, an additional attachment of the working tool disc with coupling elements can be used. However, the attachment or detachment of the working tool disc is relatively time-consuming because of the number of screw connections.
Accordingly, an object of the present invention is to provide a tool holder of the type described in which the above-mentioned drawback of the known tool holder is eliminated.
Another object of the present invention is to provide a tool holder of the above-described type which would insure transmission of a high torque between the working tool holding member and disc-shaped working tool together with an easier attachment and detachment of the working tool.